An internal combustion engine may include one or more turbochargers for compressing a fluid which is supplied to one or more combustion chambers within corresponding combustion cylinders. Each turbocharger typically includes a turbine driven by exhaust gases of the engine and a compressor which is driven by the turbine. The compressor receives the fluid to be compressed and supplies the compressed fluid to the combustion chambers. The fluid which is compressed by the compressor may be in the form of combustion air or a fuel and air mixture.
It is known to provide multiple turbochargers within a turbocharger system in an internal combustion engine. For example, U.S. Pat. No. 3,250,068 (Vulliamy) discloses an internal combustion engine having two turbochargers. A first turbocharger includes a turbine which is driven by a single exhaust manifold on the internal combustion engine. The spent exhaust gas from the turbine of the first turbocharger is transported in a series manner to the inlet of a turbine of the second turbocharger. The spent exhaust gas is then discharged to the ambient environment from the turbine of the second turbocharger. The compressor of the second turbocharger compresses ambient combustion air and provides the compressed combustion air in a series manner to the compressor of the first turbocharger, which in turn transports the compressed combustion air to the intake manifold of the engine.
An exhaust gas recirculation (EGR) system is used for controlling the generation of undesirable pollutant gases and particulate matter in the operation of internal combustion engines. Such systems have proven particularly useful in internal combustion engines used in motor vehicles such as passenger cars, light duty trucks, and other on-road motor equipment. EGR systems primarily recirculate the exhaust gas by-products into the intake air supply of the internal combustion engine. The exhaust gas which is reintroduced to the engine cylinder reduces the concentration of oxygen therein, which in turn lowers the maximum combustion temperature within the cylinder and slows the chemical reaction of the combustion process, decreasing the formation of nitrous oxides (NOx). Furthermore, the exhaust gases typically contain unburned hydrocarbons which are burned on reintroduction into the engine cylinder, which further reduces the emission of exhaust gas by-products which would be emitted as undesirable pollutants from the internal combustion engine.
With an EGR system as described above, it is known to control the amount of exhaust gas which is mixed with the combustion air for introduction into the intake manifold. Typically, a mixer such as a venturi-type mixer or the like is utilized to control the amount of exhaust gas which mixes with the combustion air. However, controlling the amount of exhaust gas which mixes with the combustion air using only a mixer may not be sufficient to provide fine adjustments to the combustion air to exhaust gas mixture ratio.
The present invention is directed to overcoming one or more of the problems as set forth above.